Spring rates

sambo · #1 (**permalink**) 06-12-2008, 08:16 PM

Just wondering what front/rear spring rates are commonly used on street Cobras? I'm more interested in what has been fitted to Chev gen 3/4 powered Harrisons (eg, sub 1100kg), but any info is appreciated at this stage.

Thanks,
Paul

Tenrocca · #2 (**permalink**) 06-12-2008, 08:43 PM

Sambo - check out this site for online calculators.

http://www.swayaway.com/TechRoom.php

Due to the different suspension geometries, it is difficult to compare spring rates between different manufacturers. eg. think about the different force you would apply to the spring if it was mounted close to the hub, as opposed to half way along the arm - all these things need to be taken into account. i would see what fellow Harrison guys have used, and Im sure harrison has suggested rates?

Cheers,

400TT · #3 (**permalink**) 06-12-2008, 08:50 PM

Paul, exactly as Tenrocca said.

Warwick will be your best guide. The Harrisons have been tweaked and changed so much over the years that most of the spring rates from the older cars would not be ideal on the newer cars.

Plus it comes down to personal preference, how you like the car to feel. Some people even for the track prefer softer spring rates and use sway bars for control...

sambo · #4 (**permalink**) 06-12-2008, 09:10 PM

Thanks guys. I know there is a recommended setup but as Craig points out, people often make changes to suit their personal tastes and intended use. I'm trying to get a feel for the options in order to make a more informed choice.

What about these AVOs... a lot of people haven't heard of them. I've used Konis in the past and they seemed allright, but not as affordable.

400TT · #5 (**permalink**) 06-12-2008, 11:56 PM

AVO's are cheap, but not great. They do the job for most people though.

On the RCR's we are using QA1's. The double adjustable units are a work of art. Even the QA1 springs are nicely coated in silver.

sambo · #6 (**permalink**) 06-13-2008, 12:34 AM

I was looking at QA1s originally, made in the States I think? I found they didn't offer the exact open/closed lengths to match the AVOs recommended by Harrison but I might have another look as the ones I'm getting from Philm are an inch longer. Warwick said they offer the same amount of travel.

400TT · #7 (**permalink**) 06-13-2008, 01:11 AM

If you are not going to do extensive track work Phil's AVO's will do the job fine. And I expect the price is right.

Mando · #8 (**permalink**) 06-13-2008, 03:13 AM

Craigs right, AVOs are VERY average at best. If you have the cash dont scrimp on shocks, and the other Harrison owners will give you the best advice on spring rates,

Regards.

sambo · #9 (**permalink**) 06-13-2008, 07:49 PM

Quote:

Originally Posted by 400TT

And I expect the price is right.

Better than right - he's a very generous man!

sambo · #10 (**permalink**) 06-22-2009, 06:58 PM

Hi folks. Dragging this old thread up as I botched my original order with King Springs and they're kindly exchanging them. So I get it right, I've spoken to a few people and (thanks Rob) arrived at the following for my car:

Back: free height 300mm (12"), 250 lbs, inside dia 65mm.
Front: free height 250mm (10"), 275 lbs, inside dia 65mm.

Anybody with a Harrison and gen 3/4 (80 kgs lighter than Ford at front), how do those numbers look?

While we're at it, shocker height... 17" back and 14 or 15" front. How does that sound? I'm looking at QA1s at this stage.

Sambo

Tenrocca · #11 (**permalink**) 06-22-2009, 07:06 PM

Quote:

Originally Posted by sambo

While we're at it, shocker height... 17" back and 14 or 15" front. How does that sound? I'm looking at QA1s at this stage.

Sambo

Check your min and max lengths. Jack the car up and move it through the full range, measuringing the distance between mounting points at full droop and full bump. You need to make sure your suspension doesnt foul or bind at the extremes with whatever length you choose. Remember as well the fully compressed length they quote may be a bit smaller then actual as you need to add in the bump stops.

Cheers

sambo · #12 (**permalink**) 06-23-2009, 05:56 AM

Thanks Andrew - good advice and I'll be checking all that when the time comes to order shocks.

Are there any Harrison / LS owners who know what springs are in their car? I'm interested to hear whether you went with Warwick's recommendation which I believe is too hard for general road use, or have experimented with your own settings?

OZVENOM · #13 (**permalink**) 06-23-2009, 06:10 AM

imho the the best combination is 350 to 450 lbs in the front
and around 200 lbs for the rear with irs and may be 225 for a live axle.
when you fit the springs you should not have to pre load them to hold the car up if you have to wind them up to get the car up they are too soft a spring. also the angle that the shock leans over at will affect the rate when i moved my suspension out the shock leaned over at 30 deg so i had to use a 600 lb spring to get the 450 that i originaly had.

oz.

stiffy · #14 (**permalink**) 06-23-2009, 03:54 PM

Sambo,

As you car will be more of a driver than track car maybe look at the GAZ shocks with suitable springs (mine are yellow

) thats all I can tell you....... The GAZ shocks are adjustable (via circular knob).

STIFFY

*Cobber* · #15 (**permalink**) 06-23-2009, 06:28 PM

You will need to know your suspension type, sprung weight, unsprung weight and spring angle then calculate. By playing with the spring angle in the calculator and the motion ratio it is easy to see what a difference it makes.

It's not something we like to talk about but you want about 40 - 50% droop

Simply jack the car up and use a set of bathroom scales to weigh the unsprung weight of each corner. Sprung weight is a bit harder and may require a trip to the weigh bridge or an educated guess.

I used this method and it is spot on and my car sits and rides perfect.

QA1 shocks and springs get the big thumbs up from me.

Dynamic weight distribution is a whole other topic.

sambo · #16 (**permalink**) 06-23-2009, 07:37 PM

Thanks Stiffy. Never heard of GAZ - more confusion to be had there!

Cobber, which QA1s did you fit?

*Cobber* · #17 (**permalink**) 06-23-2009, 08:58 PM

I used 6 of these shocks The Jag rear uses 4 shocks.

The $ is dropping a bit but they are still good value. Summit also have the full range of springs.

Rob. Smith · #18 (**permalink**) 06-26-2009, 07:38 AM

I had a nice chat with King Springs and they admitted that they couldn't calculate a correct spring rate. They said that they just shortened their springs for production vehicles to lower them and used a thicker wire to make them stiffer. NO science, just hit and miss. As the calculation of a correct spring rate is pretty complicated the main decider is the actual spring frequency. This decides whether the car rides like a limo or a formula 1. I can't find a correct reference / comparison for a spring frequency. This crucial element is related to vehicle weight, size, performance requirement and ride comfort. How do you determine ride comfort ? I calculated my springs at 120 cycles per minute. 2 hertz, 12.556 Radians per second. This gave me a ride like a normal car but handling like a sports car....this is still in experimental and I have yet to incorporate the sway bars....I bought King springs to suit the 'rate' but had to add spacers to make up the travel...the rate was a ball park figure as King springs couldn't match what I asked for. cheap and nasty.